Eran Levin is a postdoctoral researcher at the University of Arizona, and has previously written for my blog on the topic of how blacklighting works. Here he shares some of the work he did over his PhD on and intriguing system- bats that can hibernate at room temperature, how they might do it, and what this might mean for us humans.

Preying on ants must be a frustrating life style. They are small and hard to collect, tough to chew, full of formic acid, aggressive and not very nutritious. But all of this is only true for the ant workers- the queen ants are juicy, loaded with fat (up to 50% of their body mass) and are huge in size compared with worker ants. Virgin queen ants leave their “mothers’ nest” and come above ground only once in their lifetime- for the nuptial flight. This flight is usually synchronized with all the other nests in the region by meteorological events like rain or an extremely warm day. Simultaneously, from all the nests, winged males and queen emerge, take off into the air and mate. The queens will mate sometimes with multiple males. After mating, males die and queens drop off their wings and dig themselves into the ground to establish a new colony. These queens might live up to 25 years using the same sperm from this one nuptial flight to lay hundred thousands of eggs.

There is one mammal that has synchronized its life cycle with ant nuptial flight- the greater mouse tailed bat (Rhinopoma microphyllum). This is a subtropical bat species that migrates to the north of Israel in late May. During the summer male and females are sexually segregated- males inhabit higher elevation and female stay in the warm Jordan valley. They both feed on variety of flying insects like beetles, bugs and moths, but from the first week of July they change their diet preference and start consuming almost solely the queens of the carpenter ant Camponotus sanctus. The mouse tailed bats forage for ants swarming in large groups and catch them on the wing. These very large ants have sharp mandibles and can spray formic acid. Many times a bat has lost his eye as a result of this, or an ant head has been found attached to the bat lips like a piercing.

Bat with its 'ant piercing'

While consuming ants, the body mass of the mouse-tailed bats rises fast. They accumulate huge amounts of fat in the base of their tails; sometimes doubling their body mass with fat in only three weeks. But what is so special about these ants? Like many bats, mouse-tailed bats go into hibernation during winter. For a successful hibernation, mammals should accumulate large amounts of fat in their body to serve as fuel for basic functions during the few months of hibernation fasting. However, it’s not just the amount of fat that’s important for hibernation, it’s also the composition of that fat. During hibernation the body temperature drops with the environmental temperature. In many mammals body temperature during hibernation goes under 5°C. Saturated fatty acids become solid at such low temperatures (just like how butter goes hard in the fridge). Hibernators will benefit from accumulation of unsaturated fatty acids which stay in liquid form in low temperatures. But we discovered the opposite in mouse-tailed bats- the queen ants they eat contain almost no poly-unsaturated acids. Actually, the composition of the mouse tailed body fat is the most saturated we know among mammals. So how do they survive winter?

During winter mouse tailed bats move to special warm caves along the Jordan Valley. In these caves the temperature never drops under 20C (68F) during winter. The bats stay in these caves for 5 months without eating or drinking. We suggest that the special highly saturated diet is beneficial in such hot temperatures for hibernation. We used to think about hibernation as something related to freezing temperatures, but mouse tailed bats definitely change this perception: hibernation is possible at room temperature and it is probably also related to diet composition. Induction of hibernation in humans is still impossible and would be very important for long journeys into space and to “freeze” people suffering from still incurable diseases. The ability of the mouse tailed bat to hibernate at room temperature makes it a great model organism to understand hibernation and perhaps one day apply it to humans.